Magnetic transducer with clamped body sections to hold core pieces



Dec. 1 6. 1969 L. E. KRONFELD 3,484,562

MAGNETIC TRANSDUCER WITH CLAMPED BODY SECTIONS TO HOLD CORE PIECES Filed Sept. 21, 1966 INVENTOR. LEON/4RD E. KRo/vFEw A 7' TOQNE Y5 y/MK United States Patent 5,484,562 MAGNETIC TRANSDUCER WITH CLAMPED BODY SECTIONS TO HOLD CORE PIECES Leonard E. Kronfeid, Minneapolis, Minn, assignor to The Nortronics Company, Inc., Minneapolis, Minn, a

corporation of Minnesota Filed Sept. 21, 1966, Ser. No. 580,981 Int. Cl. Gllb 5/00; Gold /12 US. Cl. 179-1002 5 Claims ABSTRACT OF THE DISCLOSURE A magnetic transducer is disclosed having a pair of body sections each containing a pair of magnetic core pieces having fiat tips thereon adapted to be urged toward abutting relationship to form a pair of magnetic circuits. A pair of spring clamping means is provided to hold the two body sections in the abutting relationship. Each spring clamping means includes a piece of resilient material having a generally flat central portion and a pair of legs that converge to produce a force therebetween. The pair of spring clamping means partially surround the body sections from opposite sides thereof and cooperate with the body sections to properly align the core pieces.

This invention pertains to new and improved magnetic transducers and clamping means for use with core hoders in magnetic transducers and more particularly to adjustable clamping means for maintaining core holders and the associated core pieces in a desired relative position prior to permanent potting or the like.

In the magnetic transducer industry devices referred to as core holders are utilized to maintain the magnetic cores of the transducers in a desired position during assembly, which core holders are integrated into the finished transducer. The core holders are constructed in a large variety of forms but in general they are hollow and somewhat rectangular shaped with one side thereof open. Each of the core holders contains at least one generally U- shaped core piece. The core pieces are fixedly positioned in the associated core holder so that the tips, which are the extreme fiat surfaces at the ends of the core pieces bordering on the magnetic flux gaps, extend outwardly into the open side of the core holder. The core tips and certain pads or portions of the open side of the core holder are lapped and polished to place them as closely in a plane as possible. In some instances the manufacturer attempts to place the core tips and the pads in a common plane and in some instances the core tips are in a plane spaced from a plane through the pads. It might be mentioned that the present invention is especially useful in the latter instance; however, this is not critical to the present invention and will not be elaborated upon further. In general the assembled core holder and associated core pieces make up a body-section that is usually a half-section two of which are joined with the open sides thereof in juxtaposition to form a transducer. A magnetic flux gap is formed between the front core tips of mating core pieces in a transducer the dimensions of which are very critical to the magnetic characteristics thereof. The relative positions of the rear core tips is generally important also, however, the magnetic finx gap between the front core tips is the gap usually utilized for tape contact and, therefore, to simplify this disclosure the front core tips will be referred to simply as core tips with the understanding that the rear core tips rre included where appropriate. It can be seen that the relative positions or alignment of the core tips is very important and has a substantial eflect on the magnetic characteristics of the magnetic flux gap.

In the prior art the half-sections are generally fixedly attached together by some means such as screws or the 3,484,562 Patented Dec. 16, 1969 "ice like. Holes are formed in the core holders perpendicular to the open side and adjacent the edges, which holes are adapted to receive screws therein. The hole in one core holder is generally tapped and the mating hole in the opposite core holder is adapted to receive the body of the screw. It can be seen that once the core pieces are fixed in the core holders and the screw holes are formed the relative positions of the core tips are determined and only very slight variations can be accomplished under the best of conditions. Therefore, a slight variation in the position of the core pieces within the core holder relative to the screw holes will greatly affect the relative positions of the core tips and, therefore, the magnetic characteristics of the magnetic transducer. The close tolerances which must be maintained in providing screw holes and the the like in the core holders greatly increases the difficulty and cost of production thereof.

The screws and screw holes or other clamping means are generally situated at the edges of the core holders thereby applying pressure at the edges or corners of the assembled half-sections of a transducer. When two halfsections are assembled into a transducer the screws are tightened by a torque wrench or other torque measuring device in an effort to produce substantially equal forces on the half-sections by each screw. However, because of varying friction between the screws and the threads in the core holders and the mating surface condition between the screw head and core holder surface the amount of force produced by each screw cannot be accurately measured. Thus, in many instances the forces produced by the different screws in a single transducer vary considerably. This variation in the forces produces a pressure differential across the transducer which in many instances causes slight distortions of the half-sections and subsequent changes in the relative positions of the core tips. Thus, it is extremely difiicult to produce large groups of transducers having the same or substantially the same magnetic characteristics.

In the present invention a clamping means is utilized which adjustably holds the body-sections together. It should be noted that the clamping means will operate in transducers made up of multi-sections other than halfsections, such as third sections or quarter sections, and half sections are simply used for explanational purposes in the following specification. It should also be noted that usually the core pieces are generally U-shaped but when body-sections other than half-sections are utilized the core pieces might be simply in the form of a bar. Whatever the shape of the core piece a fiat portion or tip thereof cooperates with a similar flat portion or tip on a mating core piece to produce a magnetic circuit and flux gap. For purposes of this invention a core piece is any of the various embodiments employed or that may be employed and a core tip is the portion of the core piece bordering the magnetic flux gap. The clamping means and the core holders are constructed so that reference areas may be utilized during assembly of the half-sections which reference areas will provide sufficient alignment of the core tips for the general application. However, if a higher degree of alignment is desired, the relative positions of the half-sections may be varied after assembly to more closely align. the core tips. Once the half-sections are assembled and the desired alignment is achieved a small amount of adhesive is applied to the clamping means and the halfsections to maintain the relative positions during the remainder of the assembly.

In addition to being adjustable the clamping means applies uniform forces at predetermined areas of the halfsections urging the half-sections and the core pieces contained therein together. The instant clamping means is constructed so that the force it produces can be easily controlled to a given amount and tolerance. Also, the

force is directed against the half-sections laterally inwardly from the edges as opposed to adjacent the edges as in the prior art. In the preferred embodiment forces are directed inwardly on each half-section at approximately the midpoints of the core pieces contained therein. Thus, the clamping means urges the core tips together uniformly and there is no danger of distortion due to nonuniform or too great a force on the half-sections. Since the force of each clamping means and the position of the clamping means relative to the half-sections can be closely controlled, groups of transducers can be constructed wherein each transducer in the group has magnetic characteristics substantially similar to any other transducer in the group. In addition to the above advantages core holders having configurations or materials which make screws or other prior art clamping devices impractical can be utilized in conjunction with the present clamping means.

' It is an object of the present invention to provide an improved magnetic transducer.

It is a further object of the present invention to provide a new and improved clamping means for use with body-sections of a transducer.

It is a further object of the present invention to provide clamping means for use with body-sections of transducers which apply uniform clamping forces to the bodysections laterally inwardly from the edges thereof to produce transducers having consistent magnetic characteristics.

It is a further object of the present invention to provide an adjustable clamping means which allows accurate alignment of the core tips during assembly of the bodysections into a transducer.

It is a further object of the present invention to provide a clamping means which is inexpensive to manufacture and easy to assemble.

It is a further object of the present invention to provide a clamping means in which the manufacturing tolerances are easier to maintain.

These and other objects of this invention will become apparent to those skilled in the art upon consideration of the accompanying specification, claims and drawings.

Referring to the drawings, wherein like characters indicate like parts throughout the figures:

FIG. 1 is a view in perspective of the present clamping means assembled with two half-sections;

FIG. 2 is a view in perspective of a single spring clamping device;

FIG. 3 is an exploded view in perspective illustrating typical reference shoulders on the core holders;

FIG. 4 is an enlarged front view of the two half-sections with the clamping means assembled thereon;

FIG. 5 is a front view similar to FIG. 4 illustrating a slight misalignment of the core tips along an axis perpendicular to a plane containing the core pieces; and

FIG. 6 is a side view of the magnetic transducer illustrated in FIG. 4 illustrating a misalignment of the core tips along a line lying in the plane of the core pieces.

In the figures the numeral 10 generally indicates a transducer including a first half-section 11 and a second half-section 12. Transducer 10 is not illustrated in its finished state since there is generally a case, which operates as a shield, placed over the entire assembly and the openings in the case are then filled with a potting material to rigidly fix the entire assembly therein. However, since this is not a portion of this invention, it will not be discussed further. In general the half-sections 11 and 12 of the transducer 10 are mirror images of each other and are adapted to be urged together into abutting relationship. In the present embodiment two cores 14 and 15 are illustrated each of which is comprised of two generally U- shaped pieces designated 14a, 14b, and 15a, 15b. The U-shaped core pieces 14a and 15a are fixedly mounted in a core holder 11 and the U-shaped core pieces 14b and 15b are fixedly mounted in a core holder 12. The combination of the core holder 11' and the core pieces 14a and 15a constitute the half-section 11 and the combination of the core holder 12 and the core pieces 14b and 15b constitute the half-section 12. Adjacent sides of the core holders 11 and 12 are open and the core pieces 14a, 14b, 15a and 1511 are mounted therein so the tips extend outwardly into the open side. The rear tips of core pieces 14a, 14b, 15a and 15b, which are not shown and will not be discussed in this specification, might be placed in a number of relative positions all of which are intended to come within the scope of this invention. Normally the rear tips are in closely adjacent or in abutting relationship to provide a minimum or no back gap. Mating front tips of th core pieces 14a, 14b, 15a, 15b generally have a gap spacer provided therebetween in some fashion and when the half-sections 11 and 12 are urged together a flux gap is formed thereby. The gap spacer is not illustrated in the figures since it is generally very thin and in some cases may not be utilized at all. Normally present conventional transducers utilize a gap formed by vacuum depositing a thin film of non-magnetic material on one or both core piece tips or by inserting a thin strip of non-magnetic material therebetween. It should be understood that the present transducer 10 is utilized simply for explanatory purposes and the present invention would operate in many other transducers, including transducers having more than two body-sections.

In FIG. 2 a single spring clamping device 20 is illustrated. The spring clamping device 20 is constructed from a fiat piece of resilient material, which may be any suitable material that provides the features or functions of this invention. In the present embodiment the spring clamping device 20 is constructed from a beryllium-copper alloy. The spring clamping device 20 is formed into a generally U-shape having a first leg 21, a bight or central portion 22 and a second leg 23. The extreme ends or edges of the legs 21 and 23 are designated 24 and 25 respectively. When the spring clamping device 20 is in an unstressed position, as illustrated in FIG. 2, the legs 21 and 23 are bent at an angle from the central portion 22 toward each other so that the device 20 is somewhat C-shaped. The shape and tensile strength of the clamping device 20 is such that the central portion 22 is flat and the legs 21 and 23 are almost parallel but converge slightly when the clamping device 20 is correctly positioned over the halfsections 11 and 12. Preferably as shown, the corners of the spring and adjacent core holders do not engage and interfere with proper positioning and functioning of the spring. Thus, when the spring clamping device 20 is placed over the half-sections 11 and 12 so that the legs 21 and 23 are sprung outwardly to a position at which they are almost parallel but converge slightly, the major portion of the spring force is at the ends 24 and 25 of the legs 21 and 23. The legs 21 and 23 of the spring clamping device 20 should always be somewhat convergent so that the spring force is at or near the ends 24 and 25 and, therefore, spaced laterally inwardly from the edges of the half-sections 11 and 12. It should be noted that various configurations of the spring clamping devices might be devised (especially where space in the transducer is not a problem) wherein the legs are parallel or even diverge but the force is still directed to opposite sides of the transducer. All such configurations are included within the scope of this invention although not specifically described herein.

Referring to FIG. 3 the transducer 10 is illustrated with the right half-section designated 11 and the left halfsection designated 12. Since the half-sections 11 and 12 are as similar as possible through the production methods utilized only the left half-section 12 will be described in detail. The half-section 12 is substantially rectangularly shaped with the left side designated 30, the upper side designated 31, the front side designated 32 and the lower side designated 33. The inner or open side, not

shown, which lies in juxtaposition to the inner or open side of the half-section 11 will not be described in detail since it does not form a part of this invention. Also, the rear sides of the half-sections 11 and 12 are open and have a plurality of guides 34 extending rearwardly. A terminal board 35 having four terminals or connecting pins 36 extending rearwardly therefrom is positioned in the open rear portion of the transducer between the guides 34 and held in place by the guides 34. The pins 36 on the terminal board 35 are attached to the coils, not shown, on the cores 14 and 15.

A shoulder 40 is formed in the half-section 12 a portion of which extends across the upper side 31 perpendicular to the side 30 and a portion of which extends downwardly across the side 30 perpendicular to the side 31 approximately one-third of the width of the side 30. In a similar fashion a second shoulder 41 is formed in the half-section 12 a portion of which extends across the lower side 33 perpendicular to the side 30 and a portion of which extends across the side 30 perpendicular to the side 31 approximately one-third of the width of the side 30. The shoulders 40 and 41 are such that there is a step up or outward from the front portion of the sides 31 and 33 to the rear portion thereof. It should be understood that these dimensions are not critical and are simply mentioned for descriptive purposes. Thus, the ends of the shoulders 40 and 41 are spaced apart approximately one-third of the width of the side 30. A pair of parallel, spaced apart shoulders 42 and 43 extend from the ends of the shoulders 40 and 41, respectively, approximately to the front side 32. In this embodiment the thicker portion of the core holder 12' between the spaced apart shoulders 42 and 43 acts to reinforce the half-section 12 and add extra strength thereto. The thicker portion of the core holder 12 is an added feature which is not necessary to all constructions of my invention and the side 30 might be formed in a signal thickness. The shoulders 42 and 43 are oriented in the same direction as the shoulders 40 and 41 so that when the two half-sections 11 and 12 of the transducer 10 are placed in their proper relative positions a single continuous shoulder is formed from the front side 32 of the half-section 12 rearwardly to approximately the center thereof and then perpendicular upwardly and over the upper sides 31 of the half-sections 12 and 11, after which the shoulder extends downwardly across the opposite side of the half-section 11 and forward to its front side. Similarly a second continuous shoulder is formed across the left and right sides 30 and the bottom sides 33 of the half-sections 11 and 12. As will be apparent presently, the shoulders 42 and 43 and parts of the shoulders 40 and 41 lying in the side 30 are not necessary to this embodiment of the invention and are only included in this embodiment so the legs 21 and 23 will not protrude substantially past the outer surface of the side 30 and interfere with subsequent assembly procedures.

The central portion 22 of the spring clamping device 20 is somewhat greater than the combined lengths of that portion of shoulder 40 on the sides 31 of the halfsections 11 and 12. The portion of the shoulder 40 extending downwardly on the side 30 of the half-section 12 is somewhat longer than the length of the leg 21 while the portion of the shoulder 40 extending downwardly on the corresponding side of the half-section 11 is somewhat longer than the length of the leg 23 of the spring clamping device 20. To engage the spring clamping device '20 on the transducer 10 the legs 21 and 23 are spread apart and the spring clamping device 20 is placed over the transducer 10 so that the central portion 22 thereof is parallel and in juxtaposition to the sides 31. For initial assembly the portion 22 is fiat against both of the sides 31 of the half-sections 11 and 12 and the entire rear edge of the clamping device 20 is placed in abutment with the shoulder 40. However, it should be noted that only a portion of the rear edge, such as for example the rear edge of the central portion 22 or the rear edge of the legs 21 and 23, might be utilized for alignment. If the rear edge of the legs 21 and 23 are utilized for alignment, portions of shoulders 40 and 41 lying in the side 30 are provided for abutment therewith. A second clamping device 20', which is in all respects similar to the clamping device 20, is then placed over the lower side 33 of the transducer 10 so that the portion 22 is flat against both of the sides 33 of the half-sections 11 and 12 while one entire edge thereof is in abutment with the shoulder 41. In practice both clamping devices 20 and 20' might be applied simultaneously. FIG. 1 illustrates both spring clamping devices 20 and 20 in the position described.

When the spring clamping devices 20 and 20' are correctly positioned over the half-sections 11 and 12 the forces produced adjacent the ends 24, 25, and 24, 25' are directed approximately perpendicular to the sides 30 of the half-sections 11 and 12 and laterally inwardly from the edges thereof. In this embodiment the cores 14 and are positioned at an angle with the front side 32 so as to diverge as they extend rearwardly. Since the ends 24, 25 and 24' and 25 of the spring clamping devices and 21) are approximately perpendicular to the front side 32 they cannot be positioned over the cores 14 and 15 along the entire width of the clamping devices 20 and 20, although this might be possible in some different embodiment. However, in the disclosed embodiment the spring camping devices 20 and 20 are designed so the ends 24, and 24', 25' are positioned over each of the core pieces 14a, 14b and 15a and 15b and intersect lines which extend approximately through the mid-points of the respective core pieces 14a, 14b and 15a, 15b and lie perpendicular to the tips thereof. This position of the clamping devices 20 and 20' directs the spring forces toward the midpoints of the core pieces 14a, 14b and 15a, 15b to urge the tips thereof uniformly together. It should be understood that in certain embodiments of this invention the ends 24, 25 and 24, 25' of the clamping devices '20 and 20 might be positioned over portions of the half-sections 11 and 12 so as to intersect the described lines through the midpoints of the cores 14 and 15 but which are displaced laterally inwardly from the edges of the sides and urge the tips of the cores 14 and 15 substantially uniformly together. While the former embodiment is preferred the later embodiments are within the scope of this invention.

Placing the rear edges, or a preferred portion thereof, of the clamping devices 20 and 20' against the shoulders 40 and 41 of both half-sections 11 and 12 generally correctly positions the half-sections 11 and 12 and the tips of the core pieces 14a, 14b, and 15a, 15b relative to each other in a direction perpendicular to a plane containing the shoulders 40 and 41. Placing the central portions 22 and 22 of the clamping devices 20 and 20' parallel and against the upper and lower sides 31 and 33 of both half-sections 11 and 12 generally correctly positions the half-sections 11 and 12 and the tips of the core pieces 14a, 14b and 15a, 15b relative to each other in a direction perpendicular to the central portions 22 and 22'. Thus, the two half-sections 11 and 12 and the tips of the cores 14 and 15 are correctly aligned for most applications by positioning the clamping devices 20 and 20, as described above. For a more accurate alignment of the tips of the cores 14 and 15 the relative positions of the clamping devices 20 and 20' and the half-sections 11 and 12 can be altered slightly as described in more detail presently.

It should be noted that in all of the figures a hole 45 is illustrated in the upper front corner of each of the half-sections 11 and 12, which hole 45 extends through the half-sections 11 and 12 perpendicular to the side 30. Likewise a hole 46 is illustrated in the lower front corner of each of the half-sections 11 and 12 extending perpendicular to the side 30. These holes 45 and 46 illustrate the most common prior art method of fixedly joining the half-sections 11 and 12 during assembly, and are illustrated only for comparison with the clamping means of this invention and not because they are necessary to this invention. Although not illustrated in detail, generally one hole 45 is tapped while the mating hole 45 is adapted to receive the body of a screw. The holes 46 are similarly constructed. It can be seen that variations in the distance between the cores 14 and 15 and the holes 45 and 46 in the half-sections 11 and 12, due to tolerance variations, etc., will cause misalignment of the tips of the core pieces 14a, 14b, and 15a, 15b.

FIG. 4 illustrates the ideal situation Where the clamping devices 2'19 and 20' are in the initial assembly position and the tips of the core pieces 14a, 14b and 15a, 15!) are in exact alignment. However, because of tolerances in the construction of the half-sections 11 and 12 the tips of the cores 14 and 15 will rarely be in exact alignment but Will generally be misaligned slightly. The position of the cores 14 and 15 with respect to the shoulders 40 and 41 and the sides 31 and 33 will in general be held to a close enough tolerance so that the spring clamping devices 20 and 20 can simply remain in the initial assembly position and the tips of the core pieces 14a, 14b and 15a, 15b will be in sufficiently close alignment.

In some instances it is desirable to align the tips of the core pieces 14a, 14b and 15a, 1512 more accurately than the initial or general assembly can provide. Referring to FIGS. 5 and 6 two possible core tip misalignments are illustrated. In FIG. 5 the tips of the core pieces 14a, 14b and a, 15b are aligned but the core holders 11 and 12' are misaligned. It can be seen that in this particular transducer the holes 45 and 46 in the half-section 12 are not aligned with the holes 45 and 46 in the half-section 11 when the tips of the core pieces 14a, 14b and 15a, 1512 are aligned. Therefore, if the half-sections 11 and 12 illustrated in FIG. 5 were assembled with screws, there would normally be a considerable misalignment of the tips of the core pieces 14a, 14b and 15a, 1515. There are ways and means to accomplish alignment of the core tips with screws, but it is time consuming, extremely difiicult, and

generally requires extra and special equipment. However,

by assembling the same transducer with the spring clamping devices and 20', a slight adjustment can be made after assembly to align the tips of the core pieces 14a, 14b and 15a, 15b. This adjustment can be seen by noting that the central portion 22 of spring clamping device 29 does not lie flat against the side 31 of the half-section 12 and the central portion 22 of the clamping device 20' does not lie fiat against the side 33 of the half-section 11. The pressure applied to the half-sections 11 and 12 by the spring clamping devices 20 and 2t? maintains the half-sections 11 and 12 in the relative positions in which they are placed by the assembler and allow relative movement after assembly for more exact alignment. Thus, the spring clamping devices 29 and 20 make a very accurate alignment easier and more readily accomplished than in any prior art construction.

In FIG. 6 the tips of the core pieces 14a, 14b and 15a, 151) (not shown) are aligned even though the half-sections 11 and 12 and the associated screw holes 45 are misaligned. In this particular transducer the spring ciamping device 21 is in abutment with the shoulder 40 on the half-section 11 but is removed slightly from the shoulder 40 on the half-section 12. Thus, FIGS. 5 and 6 illustrate that the spring clamping devices 20 and 20 provide for an eflective relative movement between the half-sections 11 and 12, thereby allowing the tips of the core pieces 14a, 14b and 15a, 15b to be aligned by the assembler.

When assembling the transducer 16, as previously explained, the legs 21 and 23 of the spring clamping device 20 are spread apart after which the device 20 is engaged over the half-sections 11 and 12 of the transducer it When the spring clamping device 26 is correctly positioned over the half-sections 11 and 12 the legs 21 and 23 return to a slightly convergent position so the force produced thereby is directed inwardly adjacent the ends 24 and 25 thereof. The ends 24 and 25 of the legs 21 and 2.3 apply pressure to the half-sections 11 and 12 laterally inwardly from the edges thereof so that the force provided by the spring clamping device 20 produces a substantially uniform pressure on the half-sections 11 and 12 tending to urge the core pieces 14a and 1412 into an abutting relationship. Similarly the spring clamping device 29 tends to urge the core pieces 15a and 15b into an abutting relationship. Once the half-sections 11 and 12 and the spring clamping devices 20 and 20 are assembled and the core tips are aligned as accurately as desired some adhesive is applied to maintain the various parts in the desired relationship until they are assembled in a case. Also, the spring clamping devices 20 and 20' have greatly simplified the assembly of the transducer 10 as well as the initial production of the core holder 11' and 12'.

What is claimed is:

1. An improvement in a magnetic transducer comprising:

(a) a transducer having a pair of body sections each containing a pair of magnetic core pieces having fiat tips thereon adapted to be urged toward abutting relationship to form a pair of magnetic circuits;

(b) spring clamping means including at least one piece of resilient material formed into a generally U-shape with a generally flat central portion when mounted on said transducer and a pair of legs;

(0) said spring clamping means being mounted on said transducer so as to partially surround said bodysections with the central portion thereof overlying corresponding flat portions of said body-sections to maintain said body-sections in a desired relative position; and

(d) said spring clamping means being further characterized by having the ends of said legs positioned so as to apply force to said body-sections for urging each of said core pieces toward an abutting relationship.

2. An improvement in a magnetic transducer as set forth in claim 1 wherein each of the body-sections has a shoulder on the outer surface thereof for relative positioning of said body-sections with an edge of the spring clamping means being parallel to said shoulders in abutting relationship with at least one of said shoulders.

3. An improvement in a magnetic transducer as set forth in claim 1 wherein the spring clamping means includes a pair of generally U-shaped resilient members mounted on the transducer.

4. An improvement in a magnetic transducer as set forth in claim 1 wherein the fiat portions of the bodysections abut said fiat central portion for relative positioning of said body-sections for core tip alignment in a first direction located in a plane parallel to the core tips and perpendicular to the fiat central portion of the spring clamping means, and in addition each body-section has a shoulder on the outer surface thereof abutting the edge of said spring ciamping means for relative positioning of said body-sections for core tip alignment in a second direction located in said plane but perpendicular to said first direction.

:5. An improvement in a magnetic transducer comprising:

(a) a transducer having a plurality of body-sections each containing at least one magnetic core piece having fiat tips thereon adapted to be urged toward abutting relationship to form a magnetic circuit;

(b) a pair of spring clamping means each comprising a piece of resilient material formed into a generally U-shape in which the legs are convergent and adapted to produce a force therebetween;

(c) said spring clamping means being mounted on said transducer so as to partially surround said bodysections, said legs remaining somewhat convergent 1n the mounted position so the force produced therebetween is adjacent the ends of said legs; and

(d) said spring clamping means being further charac- 9 10 terized by having the ends of said legs positioned 3,211,843 10/1965 Dundovic et a1. 179-100.2 so as to each intersect a line which extends through 3,370,282 2/ 1968 Baldwin et a1 340-1741 the mid-point of a core piece perpendicular to the FOREIGN PATENTS tips of said core pieces for urging each of said core pieces toward an abutting relationship and maintain- 7941978 1/1955 Great 'f f ing said body-sections in a desired relative position. 5 882,042 11/1961 Great Bntam- References Cited BERNARD KONICK, Primary Examiner UNITED STATES PATENTS JEROME P- MULLINS, Assistant Examiner 2,920,149 1/1960 Koren 179100.Z 10 5 L 2,945,216 7/1960 Gyger et a1. 340174 34 174 1; 34 74 3,156,919 11/1964 Rutter 346-74 

